The replacement of dopamine (DA) by fetal mesencephalic tissues or DA-cell transplant appears to be a rational choice for the treatment of patients with advanced Parkinson's disease. Fetal mesencephalic tissues have been used extensively in animal models of Parkinson's disease See, for example, Bjorklund, A. et al. (1979) Brain Res. 177, 555-560; Perlow, M. F. et al. (1979) Science 204,643-647; Bakay, R. A. E. et al. (1985) Appl. Neurophysiol 48, 358-361; Freed, C. R. et al. (1988) in Pharmacology and Functional Regulation of Dopaminergic Neurons, eds. Beart, P. M., Woodruff, G. and Jackson, D. M. (Macmillan Press, London) pp. 353-360; Dunnett, S. et al. (1991) in Intracerebral Transplantation in Movement Disorders, eds. Lindvall, O., Bjorkland, A. and Widner, H. (Elsevier, Amsterdam) pp 27-et seq; Freed, W. J et al. (1990) Exper. Neurol. 110, 139-166; and Kordower, J. H. et al. (1994) in Neural Transplantation, CNS Neuronal Injury and Regeneration, eds. Marwah, J., Titelbaum, H. and Prasad, K. N. (CRC Press, Fla.) pp. 17-37. These studies show varying levels of improvement of neurological deficits. The use of such tissues in advanced Parkinson's disease cases also produced variable results as reported in Freed, C. R. et al. (1990) Arch. Neurol. 47, 505-512; Lindvall, 0. et al, (1992) Arch. Neurol. 31, 155-165; Madrazo, I. et al. (1990) Arch Neurol. 47, 1281-1285; and Hitchcock, E. (1992) in Recovery from Brain Damage, eds. Rose, F. D. and Johnson, D. A. (Plenum Press, N.Y.) pp. 67-78. A double-blind study with placebo control to evaluate the efficacy of fetal tissue in the treatment of neurological symptoms in patients with advanced Parkinsonism is in progress. Apart from the issue of efficacy of allogeneic fetal central nervous system (CNS) tissue in neural transplants, the use of fetal tissue is limited by ethical, legal, tissue availability, survivability and some inherent biological problems. The latter includes the presence of donor-antigen presenting cells which may induce rejection of allogeneic grafted tissues. See Freed, C. R. et al. (1990) Arch. Neurol. 47,505-512; Lindvall, O. et al. (1992) Arch. Neurol. 31, 155-165; Madrazo, I. et al. (1990) Arch. Neurol. 47, 1281-1285; Hitchcock, E. (1992) in Recovery from Brain Damage, eds. Rose, F. D. and Johnson, D. A. (Plenum Press, N.Y.) pp. 67-78. Another biological problem is heterogeneity within the population of grafted cells. In order to overcome the above difficulties, the establishment of homogeneous populations of DA--producing neurons in vitro, free of antigen presenting cells, would be invaluable. Clonal lines of transformed (tumorigenic) DA-producing neurons, such as those described in Augusti-Tocco, G et al. (1969) Proc. Natl. Acad. Sci. USA 64, 311-315; Prasad, K. N. et al. (1973) Nature New Biol. 241, 117-119; Tumilowicz, J. J. et al. (1970) Cancer Research 30, 2110-2118; Schubert, D. et al. (1974) Nature 249, 224-227; are available and have been used in neural transplant studies, but such cells produce tumors following transplantation; therefore, they may not be useful until 100% of them are terminally differentiated prior to grafting. See Freed, W. J. et al. (1986) Exp. Brain Res. 63, 557-566; and Kordower, J. H. et al. (1987) Brain Res. 417, 85-et seq.
Recently, we have reported the production of 100% terminally differentiated murine neuroblastoma (NBP.sub.2) cells in culture. See Prasad, K. N. et al. (1994) Restor. Neurol. Neurosci. 7, 13-19. However, the efficacy of these cells in improving the neurological deficit in the rat model of Parkinson's disease is minimal at 30 days after transplantation. See Adams, F. S. et al. (1996) Neurochemical Research 21, 619-627. In an effort to establish another source of DA-producing cells, spontaneously or genetically engineered immortalized cells, which include TH-producing fibroblasts, dopamine--producing SV40 LTa gene induced transformed cells at permissive temperature and multipotent neural cells, are now available. See Rosenberg, M. B. et al. (1988) Science 242, 1575-1579; Anton, R. et al. (1994) Exp. Neurology 127, 207-218; and Ryder, E. F. et al. (1990) J Neurobiol. 21, 365-375. The grafting of these cells in animal models of Parkinson's disease has produced variable improvements in neurological deficits when assayed within 3 months of transplant. Recently, we have established an immortalized clone of rat DA--producing neurons (1RB.sub.3 AN.sub.27) by transfecting fetal mesencephalon cells with the plasmid vector pSV.sub.3.sup.neo, which carries the large T-antigen gene from SV40 virus. See Prasad, K. N. et al. (1994) In Vitro Cell. Dev. Biol. 30A, 596-603; Adams, F. S. et al. (1996) Neuro Chem Res. 21, 619-627. When these cells or differentiated NBP.sub.2 cells were grafted into the striata of 6-hydroxydopamine (6-OHDA) lesioned rats, the methamphetanine-induced turning rate was reduced in about 50% of transplanted animals at 30 days after transplantation; and there was no evidence of rejection of allogeneic cells nor tumor formation at this time. Because this observation period was considered too short for determination of the efficacy of transplanted cells in improving the neurological deficits in lesioned rats, we extended the period of observation to 6 months. In addition, we compared the relative efficacy of undifferentiated and differentiated 1RB.sub.3 AN.sub.27 cells, at improving the neurological deficits in the rat model of Parkinson's disease.